Strange Twist in Bezier Curve
Compare to the default setting of curves, twist method was changed. I'm not very sure what's this setting doing. But set it back to Minimum will solve the problem.

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Select all the points than set the Mean Tilt to 180 degree.
(Actually you can control the rotation of any point one by one. Just choose the points you want to twist than use the Tilt button from the left sidebar. Than click and drag the yellow circle.)